Vinyl stilbazoles

ABSTRACT

Vinyl pyridines including vinyl stilbazole materials and vinyl styrylpyridine oligomer materials are disclosed. These vinylpyridines form copolymers with bismaleimides which copolymers have good fire retardancy and decreased brittleness. The cure temperatures of the copolymers are substantially below the cure temperatures of the bismaleimides alone. Reinforced composites made from the cured copolymers are disclosed as well.

ORIGIN OF THE INVENTION

The invention described herein was made in the performance of work undera NASA contract and is subject to Public Law 96-517 (35 U.S.C. §200 etseq.). The contractor has not elected to retain title to the invention.

This is a division of application Ser. No. 553,339, filed Nov. 18, 1983,now U.S. Pat. No. 4,526,925.

TECHNICAL FIELD

This invention relates to vinyl pyridine group-containing compounds andoligomers, their advantageous copolymerization with bismaleimide resins,and the formation of reinforced composites based on these copolymers.

BACKGROUND

Bismaleimides are being increasingly used as matrix resins forfiber-reinforced composites, especially high-performance graphitefiber-reinforced composites. The monomers are cured by a thermallyinduced addition reaction to give highly crosslinked, void-free networkpolymers having good physical properties with higher thermal stability,higher char yield, better fire resistance and lower water absorptionthan currently-used epoxy systems.

There are problems with maleimides, however, such as solvent retentionin the prepregs, high temperatures often needed for curing withattendant distortion and high cost, and the brittleness of the polymersdue to the high crosslink density obtained in network polymers.Brittleness can be such a problem that a single minor impact can greatlyreduce the strength of a maleimide-based composite. These problems haveprevented the wide application of the carbon-reinforced maleimides inaircraft primary and secondary structures where their high strength andfire resistance is much sought after.

A number of methods have been proposed to minimize some of the aforesaidproblems. For one, the basic maleimide structure can be modified. Foranother, the bismaleimides can be copolymerized with comonomers. Thepresent invention concerns vinyl pyridine group-containing compounds andtheir incorporation as comonomers into bismaleimide resins. One of thetypes of vinyl pyridine group-containing compounds has a vinylstyrylpyridine structure, i.e., a ##STR1## structure wherein n is 1 to10, each of the R₁ is hydrogen or lower alkyl and R₂ is an organicgroup. U.S. Pat. No. 4,362,860 of Ratto et al discloses such materialsas well as the materials where R₂ is hydrogen as thermosetting polymersbut does not suggest their copolymerization with bismaleimide. RockwellInternational's Final Report (Phase I) (Aug. 18, 1980 -Nov. 30, 1981) inNASA contract NAS2-10709 further discusses the Ratto et al findingswhere R₂ is hydrogen and shows that the one step synthesis route itdiscloses gives a mixture product which must be fractionated to obtainthe desired vinyl styrylpyridine materials.

U.S. Pat. Nos. 3,810,848 and '872 disclose a family of complex-formingpolymers having ##STR2## units, wherein L is a covalent bond or O, S,CO, CHR or NR and R is hydrogen or an alkyl. At Example 6, U.S. Pat. No.3,180,848 shows condensing such a polymer with a pyromellitic anhydrideto give a maleimide-like copolymer structure. Another patent of interestis U.S. Pat. No. 3,994,862 of Ropars, et al. which disclosescondensation products of trimethylpyridine with aromatic aldehydes togive prepolymers which differ from the present vinyl-terminatedstyrylpyridines in not having the vinyl terminis. Ropars, et al. alsodoes not show copolymers with bismaleimides.

STATEMENT OF THE INVENTION

It has now been found that the properties of bismaleimide resins andtheir preparation conditions are substantially improved by incorporatingwith the bismaleimide resins, as copolymeric units, the vinyl pyridine5-vinyl-2-stilbazole of the structure ##STR3## and/or the vinylstyrylpyridine oligomer of the structure ##STR4## wherein R and R¹ areindependently selected from hydrogen, aryls, lower alkyls, alkoxy andhalos, R₁ is hydrogen or lower alkyl, and R₂ is a 1 to 4 carbon organicgroup.

In another aspect, this invention provides the vinyl stilbazolematerials as novel comonomers.

In a further aspect, this invention provides composites made up of thebismaleimide resin copolymers cured with a reinforcing amount ofreinforcing fiber. The copolymer resins can be applied as solvented"varnishes" or very advantageously as "hot melts".

In an additional aspect, the invention provides a high yield two stepsynthetic path to the vinyl styrylpyridine oligomer (II).

Yet another aspect of this invention concerns a low temperature cureprocess for the bismaleimide resins in which the above-describedcopolymers are cured at temperatures of from about 130° C. to 230° C.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described with reference being made to theaccompanying drawing in which

FIGURE is a differential scanning calorimeter plot of the relative curetemperatures of the copolymers of this invention and the individualmonomers alone.

DETAILED DESCRIPTION OF THE INVENTION

Vinyl stilbazole

The vinyl stilbazole materials of this invention have the structure##STR5## wherein each of R and R¹ are independently selected fromhydrogen; lower alkyls, alkoxy, aryls and halos, i.e., 1 to 4 carbonalkyls and alkoxy, chloros, iodos, bromos, phenyls and alkyl phenyls of7 to 9 carbons and the like, especially methyl, ethyl, isopropyl,methoxy, ethoxy, chloros, and phenyl. Preferably at least one and morepreferably both of R and R¹ are hydrogens.

Such materials are prepared by condensing 5-vinyl-2-methyl pyridine withan appropriately R and R¹ -substituted benzaldehyde under dehydratingconditions as follows: ##STR6## This reaction can be carried out neat,since the reactants are solvents for one another. A nonaqueous inertsolvent such as DMF, glacial acetic acid, NMP (N-methylpyrolidone), DMAcor DMSO could be used if desired. The dehydration conditions aresuitably provided by acetic anhydride, optionally in combination withacetic acid and/or a catalyst like ZnCl₂ to activate the methyl groups.The condensation is carried out at a temperature of from about 50° C. toabout 140° C. Higher temperatures are generally to be avoided as theymay lead to some degree of polymerization of the product. The reactionis not rapid at these temperatures, generally requiring at least about 4hours and preferably 6 to 60 hours. The reaction is preferably carriedout in the substantial absence of oxygen--either under reduced pressureor under an inert atmosphere like nitrogen or argon. Usually, aboutequimolar amounts (i.e., from 1 to 1.1 to about 1.1 to 1 moles) of thevinyl pyridine and the aldehyde are employed. An excess of one materialor the other could be employed, but the excess would only have to beremoved from the final product.

Vinyl styrylpyridine oligomers

The vinyl styrylpyridine oligomer materials have the structure ##STR7##wherein n is an integer from 1 to 10, most advantageously 1 to 4, R₁ ishydrogen or a lower alkyl of 1 to 4 carbons, especially hydrogen ormethyl, but more especially, hydrogen; and R₂ an organic group such asis a 1 to 4 carbon alkyl, or a 1 to 4 carbon alkoxy, a halo-substituted1 to 4 carbon alkyl, such as, for example, methyl, ethyl, propyl, butyl,methoxy, ethoxy, 2-chloroethyl, chloromethyl. R₂ is especially a methylor methoxy.

The structure II is an "average" structure and is provided to show arepresentative structure at the A and B rings. The exact substitutionpatterns on the A and B rings can vary. The A rings should have theirtwo double bonds in a "1,3" (meta) or "1,4" (para) configuration. The Brings should have their two olefin groups i.e. "vinyl" groups and R₂ ina "2,6-divinyl-4-R₂ " or a "2,4-divinyl-6-R₂ " configuration.

These oligomeric materials are prepared by the two step process of (1)condensing a 2,6-dimethyl-4-R₂ -pyridine or a 2,4-dimethyl-6-R₂-pyridine such as collidine, or the like with an R₁ -substitutedaromatic dialdehyde such as an "R₁ -substituted" terephthaldehyde underdehydrating conditions and in the absence of a vinyl pyridine and (2)thereafter treating the reaction product with 5-vinyl-2-methylpyridineagain under dehydrating conditions, for example: ##STR8## In the firststep of this reaction the number of equivalents of aldehyde should begreater than the number of equivalents of methyl groups on the 2 and 4or 2 and 6 positions on the dimethyl-R₂ -substituted pyridine,preferably from 1.0 to 1.5 times the number of 2,4 or 2,6 methyls. Inthe second step the combined equivalents of 2,4 or 2,6 methyls plusvinyl methylpyridine is larger than the total equivalents of aldehydes(i.e., from 1.0 to 2.0 times). As with the stilbazole materials, acatalyst like ZnCl₂ can be present if desired. The temperature forreacting the collidine or the like with the dialdehyde may be selectedin the range of about 130° to 190° C., preferably 140° to 180° C. andmore preferably about 160° C. for times of 1-40, especially 1-20 hours.An inert oxygen-free atmosphere is preferred. The coupling of vinylmethylpyridine to residual aldehyde groups is carried out at somewhatlower temperatures, e.g., 80° to 130° C., preferably 80° to 120° C. andespecially about 110° C. again for 1 to 40, and especially 1 to 20hours, preferably in an inert atmosphere. The dehydrating conditions areachieved by having a water acceptor such as an acid anhydride, e.g.acetic anhydride, in the reaction zone or by permitting the water thatis formed to evaporate. This two step process has the advantage ofallowing precise control of each of the two reactions. In comparison tothe one step process of Ratto et al U.S. Pat. No. 4,362,860, thisprocess gives a more reproducible product in higher yield.

The Bismaleimides

The bismaleimide is represented structurally by the formula ##STR9##wherein R* and R** independently are hydrogen or a 1 to 4 carbon alkyl.Preferably R* and R** are hydrogen or CH₃ and more preferably at leastone of the groups is hydrogen. L_(Or) is a covalent organic linkinggroup, that is a bivalent organic group containing in its structure analiphatic chain or at least one aromatic ring. Many suitable examples ofthese bismaleimides are available commercially. They are preparedsynthetically by a sequenced addition of a diamine to maleic anhydridefollowed by cyclization. Bismaleimide materials can be drawn from resinshaving as L_(Or) simple ##STR10## aromatic rings as were used in thepioneering Gemon resins sold by General Electric, and ##STR11## aromaticrings as are found in commercial Kerimid 353 and Kerimid 601 resins ofRhone-Poulonc to more involved materials such as Technochemie's H-795resin: ##STR12## wherein R is an aromatic ring and X--R₁ --X is aMichael addition coupling group Technochemie's M-751 resin which is an"eutectic" mixture of ##STR13## In general, L_(Or) can be any organiclinking group that is relatively inert, that permits the bismaleimide tobe intimately admixed with the vinyl pyridine material either by meltingor by dissolving in a common solvent and that does not interfere withthe reactivity of the maleimide units. The M-795 type bismaleimidesoffer the advantage of working well in hot-melt systems.

Copolymers

The copolymers of this invention are composed of the vinylstyrylpyridine oligomers and/or vinyl stilbazole copolymerized with oneor more bismaleimides. The properties of the cured composite will dependin part of the relative amounts of the vinyl styrylpyridine oligomersand/or vinyl stilbazole and the bismaleimide. As the proportion of vinylstilbazole is increased, the product becomes less flame-resistant whenfully cured but easier to cure. As the proportion of the vinylstilbazole is increased, a more amorphous, less brittle, lesscrystalline, tougher product is achieved, but one which has decreasedflame retarding because of lesser char yield on pyrolysis.

With vinyl stilbazole the preferred maximum proportion of stilbazole isabout 2 moles per mole of bismaleimide since under the usual cureconditions the vinyl group on the stilbazole reacts with thebifunctional maleimide. With the vinyl styrylpyridine oligomermaterials, any proportion can be employed. In general, however, it isdesired to have a cured product with good flame retardency and thus toemploy at least about one mole of bismaleimide per mole of vinylstyrylpyridine and/or vinyl stilbazole. To achieve the improved productproperties, it is generally desired to use at least about 0.05 moles ofvinyl stilbazole or vinyl styryl pyridine per mole of bismaleimide. On aweight basis, it is preferred to employ maleimide to vinyl pyridineratios of 15:1 to 1:1, especially 10:1 to 2:1.

Cured Products

The cured resins of this invention find ready use as moldable plasticsand especially as binders or substrates for reinforced composites. Thereinforcement is generally a fiber and can be organic or inorganic andin organized or disorganized form, for example carbon fiber, aramidefiber or glass fiber as yarns, fabrics, or felts; or such material aschopped fiber. Other materials known in the art as polymerreinforcements, for example boron nitride, and metal fibers, can beemployed as well. Carbon fibers is the preferred reinforcement.

Conventional ratios of reinforcement to substrate are employed, such asfrom about 0.5 to about 5 parts by weight of reinforcement per part ofsubstrate.

Other materials such as fillers, pigments, antioxidants and the like canbe added as well, if desired.

Copolymer Formation and Cure

It is an important advantage of the present copolymers that their cureconditions are far less severe than those employed with thebismaleimides alone. Thus, it is less expensive to cure the presentmaterials and less distortion occurs during cure. It is also animportant advantage that the present copolymers, as they cure, do notgive off volatile components which can generate voids and decrease thestrength of the final cured products.

Copolymers are formed by admixing the bismaleimides and the vinylstyrylpyridine oligomer and/or vinyl stilbazole in the desired ratio andheating. The mixing can be carried out in a polar organic solvent suchas chloroform, tetrahydrofuran, dichloroethane, ketones such as acetone,methyl ethyl ketone, and the like, or it can be carried out using a hotmelt of the next copolymer components. This liquid mixture (or varnish)is mixed with the reinforcement, by dipping, coating or the like. Anysolvent is preferably removed prior to cure to avoid voids created bysolvent volatilizing from partially cured resin.

A typical cure cycle for a copolymer might employ 110°-170° C. to removesolvent if present (or lower temperature if vacuum is applied) and 130°to 230° C. for curing. In general the copolymers of vinyl stilbazolematerials cure at lower temperatures, i.e., 130°-190° C. than do thevinyl styrylpyridines which usually require 160°-230° C. Suchtemperatures are far lower than required for the bismaleimides alone.This can be shown experimentally using a differential scanningcalorimeter which measures heat flow and can detect when the exothermiccuring reactions take place. Three experiments were carried out in sucha calorimeter and their results are given in FIGURE.

First, a bismaleimide (Technochemie H795) was placed in the unit andheated. The peak heat flow--indicating maximum curing rate required was282.4° C. Second, vinyl stilbazole alone was tested. No distinct curepeak was detected even up to and over 400° C. In the third experiment 3parts by weight of vinyl stilbazole was mixed with 7 parts weight ofTechnochemie H795 resin. The cure temperature observed was 164° C., asshown in FIGURE. With copolymers of vinyl styrylpyridine the cure peakwould be about 200° C. These substantially reduced curing temperaturesoffer advantages of less distortion and/or shrinkage during cure andlower energy requirements.

The copolymers of this invention are formed into castings or moldedproducts by conventional processes. They can be formed into reinforcedstructural bodies by any of the methods known in the art includingpressure forming, hand layup, pull-truding, filament winding, vacuumlaminating and the like and the invention is not to be construed aslimited to any particular forming technique.

Using a representative pressure molding technique with a solvated vinylstyrylpyridine bismaleimide copolymer one might employ themelting/solvent stripping/cure cycle shown in Table I.

                  TABLE I                                                         ______________________________________                                        Mode         Temperature Pressure  Time                                       ______________________________________                                        Heat-solvent removal                                                                       150° C.                                                                            0           20   min                                 or melt mixture                                                               from hot melt                                                                 Heat and Press                                                                             180° C.                                                                            75     psi  10   min                                 Heat and Press                                                                             190° C.                                                                            100    psi  40   min                                 Heat and Press                                                                             200° C.                                                                            100    psi  200  min                                 ______________________________________                                    

Infrared analysis of a material cured by such a schedule shows that itcontains the internal double bonds of the original feedstock and thatthey have not polymerized. This is important to fire resistance as thesebonds are available to react during pyrolysis to form additional organicrings as needed for char formation.

In general, one does not have to employ curing agents or catalysts withthe present resin systems. It is often desired to not have curing takeplace during solvent removal so as to minimize or avoid forming voidsdue to the solvent release in the cured body or to maximize pot life ofa melt in which case one would prefer to not have a catalyst present. Ifthis is not considered a problem, as might be the case with injectionmolded parts, any conventional peroxide or other free-radical initiatorcan be employed as catalyst.

The invention will be further described by the following preparationsand examples. These are provided to illustrate the invention and are notto be construed as limiting its scope which is instead defined by theclaims.

Preparation I: Two Step Preparation of Vinyl TerminatedPolystyrylpyridine

Step 1: 18.0 g (0.3 mole) of acetic acid, 30.6 g (0.3 mole) of aceticanhydride, 20.1 g (0.15 mole) of terephthaldehyde, and 12.1 g (0.1 mole)of collidine were placed in a 500 ml, 3-necked round-bottom flaskequipped with a mechanical stirrer and a reflux condenser. After thereaction solution was deoxygenated, the flask was immersed in an oilbath and the reaction solution was heated at 130° C. to 170° C. forseveral hours. Step 2: The reaction solution was cooled to roomtemperature and 17.9 g (0.15 mole) of 5-vinyl-2-methyl pyridine wasadded. The solution was degassed again and heated to 80° C.-120° C. forseveral hours. The reaction mixture was then poured into 10% NaOHsolution. The brownish viscous product was washed with 10% NaOHsolution, then with de-ionized water until the aqueous layer testedneutral. All the water was decanted and the product was dissolved in THFand filtered. The filtrate was then poured into large quantity ofde-ionized water to precipitate out VPSP (II). This purification wasrepeated several times. Finally, the product was dried in vacuum andstored in THF. For hot melt applications, the product could be storedneat.

Preparation II: Preparation of Vinyl Stilbazole

50.0 g (0.42 mole) of 5-vinyl-2-methyl pyridine, 44.6 g (0.42 mole) ofbenzaldehyde, 25.2 g (0.42 mole) of acetic acid, and 42.9 g (0.42 mole)of acetic anhydride were placed in a 1000 ml, 3-necked round-bottomflask equipped with a mechanical stirrer and a reflux condenser. Afterthe reaction solution was deoxygenated, the flask was immersed in an oilbath and the reaction was held at 80° C.-120° C. for several days. Thereaction solution was then cooled to room temperature and poured into alarge beaker containing 10% NaOH solution. The mixture was stirred forhalf an hour and the aqueous layer was decanted. The brownish viscousproduct was washed several timed with 10% NaOH solution, then withdeioized water until the aqueous layer tested neutral. All the water wasdecanted and the product was dissolved in THF and filtered. The filtratewas then poured into large quantity of de-ionized water to precipitateout vinyl stilbazole. This purification was repeated several times.Finally, the brownish product was dried in vacuum, weighed andtransferred into a storage container using THF as solvent. For hot meltapplications, the product could be stored neat.

EXAMPLE 1

A maleimide copolymer was prepared as follows: 1 part by weight of vinylstilbazole (VST) as prepared above and 4 parts of Technochemie H795bismaleimide resin was dissolved in THF. The THF was removed to give anintimate mixture of the two comonomers. A portion of this material wasplaced in a differential scanning calorimeter and gradually heated todetect the cure temperature of 197° C. The cured material'sglass-transition temperature (Tg) was determined to be 380° C. and itspolymer decomposition temperature in N₂ was seen to begin at 400° C. Thematerial had a high char yield (43% at 800° C.) indicative of excellentflame retarding properties. It had a composite modulus at 25° C. of 15GPa and 12 GPa at 300° C.

A series of other copolymers based on H795 bismaleimide and the varyingamounts of the above-described VST or vinyl styrylpyridine (VPSP) wereprepared and similarly tested and compared with a currently favoredepoxy and the bismaleimides alone. The results which demonstrated theadvantages of the present invention are given in Table II.

                  TABLE II                                                        ______________________________________                                                    Cure                      CHAR                                                Temperature         PDT   YIELD                                               (DSC PEAK), T.sub.g (N.sub.2)                                                                           at 800                                  RESIN SYSTEM                                                                              °C.  °C.                                                                            °C.                                                                          %                                       ______________________________________                                        EPOXY (MY720)                                                                             255          250    300   30                                      BISMALEIMIDE                                                                              282         >400    400   42                                      (H795)                                                                        COPOLYMERS:                                                                   VST:H795 = 1:4                                                                            197          380    400   43                                      VST:H795 = 3:7                                                                            164                 400   36                                      VPSP:H795 = 1:9                                                                           245         >400    400   43                                      VPSP:H795 = 1:4                                                                           230         >400    400   50                                      VPSP:H795 = 3:7                                                                           226          400    400   55                                      ______________________________________                                    

EXAMPLE 2

Another portion of the various copolymers of Example 1 were formed intographite-reinforced composites.

In a typical preparation 9 ply satin-weave graphite fiber cloth washeated at 310° C. overnight to remove sizing in air. The resin system,for example VST/H795 3:7 by weight was dissolved in THF and brushed onthe fiber:

Fiber weight--245 g.

Fiber coating weight--405 g.

Excess resin (47 g) was removed when the fiber was lightly pressed togive a resin content of 31.5%. The product was press cured as follows:

1. No pressure--heated to 250° F. for 10 min to remove solvent.

2. No pressure--heated to 320° F. for 10 min to complete solventremoval.

3. At 75 psi--heated to 356° F. for 10 min.

4. At 100 psi--heated to 374° F. for 40 min.

5. At 100 psi--heated to 392° F. for 200 min.

6. Cool to room temperature with pressure.

The properties of the composite as well as other similar composites madewith other copolymer systems were evaluated and compared with H795 andVPSP alone. The results are shown in Table III.

The composites of this invention find especially advantageousapplication in structures which are exposed to extreme environments.They may be formed into primary and secondary structures for aircraft,spacecraft and the like (e.g. panels, wing spars and the like) wheretheir high performance thermal behavior is such as to minimize humanrisks.

                                      TABLE III                                   __________________________________________________________________________    MECHANICAL PROPERTIES OF VST, VPSP/BMI COPOLYMER                              COMPARED WITH H795 GRAPHITE COMPOSITES                                                        RESIN SYSTEM WITH 9 PLY SATIN-WEAVE GRAPHITE FIBER            PHYSICAL & MECHANICAL                                                                             VPSP/H795                                                                            VST/H795                                                                            VPSP/H795                                                                            VST/H795                              PROPERTIES      H 795                                                                             1:4    1:4   3:7    3:7   VPSP                            __________________________________________________________________________    RESIN CONTENT % 30.5                                                                              26     30    30.2   31.5  26                              DENSITY, g/cc   1.55                                                                              1.43   1.39  1.4    1.39  1.44                            LOI (4 PLY SAMPLE)                                                                            52  62     46    55     45    57                              WATER ABSORPTION, %                                                                           0.72                                                                              1.17   0.99  1.20   0.86  1.36                            2 hrs BOILING WATER                                                           SHORT BEAM SHEAR                                                                              1.7 2.95   2.96  2.7    2.89  3.15                            R.T. KSI                                                                      R.T. FLEXURAL                                                                 MODULUS, MSI    7.7 7.3    7.3   7.4    7.4   7.6                             STRENGTH, KSI   24  41     46    44     41    49                              FLEXURAL, 100° C.                                                      MODULUS, NSI HOT-WET                                                                          5.8 7.1    6.9   7.0    6.3   --                              STRENGTH, KSI HOT WET                                                                         24  37     44    40     37    --                              YOUNG'S MOD, GPa                                                               25° C.  15  15.5   13    15     15    --                              300° C.  14  15     12    14     13.5  --                              __________________________________________________________________________

We claim:
 1. A 5-vinyl-2-stilbazole of the structure ##STR14## wherein Rand R' are independently selected from hydrogen, lower alkyls, loweralkoxy, phenyl, alkyl phenyls of 7 to 9 carbons, chloro, bromo or iodo.2. The 5-vinyl-2-stilbazole of claim 1 wherein R and R' areindependently selected from hydrogen, methyl, ethyl or isopropyl.
 3. The5-vinyl-2-stilbazole of claim 2 wherein one of R and R' is hydrogen. 4.The 5-vinyl-2-stilbazole of claim 3 wherein the other of R and R' ismethyl.
 5. The 5-vinyl-2-stilbazole of claim 1 wherein R and R' areindependently selected from hydrogen, methoxy or ethoxy.
 6. The5-vinyl-2-stilbazole of claim 5 wherein one of R and R' is hydrogen. 7.The 5-vinyl-2-stibazole of claim 6 wherein one of R and R' is methoxy.8. The 5-vinyl-2-stilbazole of claim 1 wherein R and R' areindependently selected from hydrogen, phenyl or alkyl phenyls of 7 to 9carbons.
 9. The 5-vinyl-2-stilbazole of claim 7 wherein one of R and R'is hydrogen.
 10. The 5-vinyl-2-stilbazole of claim 1 wherein R and R'are independently selected from hydrogen or phenyl.
 11. The5-vinyl-2-stilbazole of claim 10 wherein one of R and R' is hydrogen.12. The 5-vinyl-2-stilbazole of claim 1 wherein R and R' areindependently selected from hydrogen, chloro, bromo or iodo.
 13. The5-vinyl-2-stilbazole of claim 5 wherein one of R and R' is hydrogen. 14.The 5-vinyl-2-stilbazole of claim 1 wherein R and R' are independentlyselected from hydrogen or chloro.
 15. The 5-vinyl-2-stilbazole of claim14 wherein one of R and R' is hydrogen.
 16. A 5-vinyl-2-stilbazole ofthe structure ##STR15##